An RFID reader requires significant levels of power supply current, upwards or beyond 0.5 amps. Much of this power requirement is expended to activate the reader's radio frequency transmitter. For example, the reader's transmitter may constantly be active awaiting a RFID tag entering within its electromagnetic field. This is the usual operation for readers utilized in door entry security, inventory control, shipping and receiving management, and contactless point of sale. However, sometimes an adequate power source, such as AC mains, is not available to provide continuous transmitter operation and instead a battery is used to power the reader.
Battery powered readers typically need a manual control to trigger the reader's transmitter to conserve battery capacity with the transmitter normally off until triggered. The manual control may be by a press of a button, or an insertion of a key, which then activates the reader's transmitter. This must be followed, within a few seconds, by manually placing a RFID tag within the reader's transmitted electromagnetic field before the trigger operation times-out and the transmitter turns off to conserve power.